Recently, a glass-sealed package has gained attention that includes a base substrate and a lid substrate, both made of glass, anodically bonded in layers with a cavity formed therebetween, and an active piece mounted on the base substrate in a portion inside the cavity. One known example of the glass-sealed package of this type is the piezoelectric vibrator that uses crystals or other materials for applications such as a clock source, a timing source of control signals or the like, and a reference signal source by being installed in, for example, cellular phones and personal digital assistant units.
The glass-sealed package of this type is produced by anodically bonding a base substrate wafer and a lid substrate wafer via a bonding film made of a conductive material for anodic bonding, with the wafers set in an anodic bonding machine installed in a vacuum chamber.
Specifically, the bonding face of the lid substrate wafer includes large numbers of depressions that provide cavities when the lid substrate wafer is mated with the base substrate wafer. On the bonding face of the base substrate wafer, large numbers of active pieces (for example, piezoelectric vibrating pieces) that correspond to the depressions are mounted, and a bonding film is formed on this bonding face except in portions corresponding to the depressions. The lid substrate wafer is set on an electrode plate of the anodic bonding machine.
Next, while activating the ions in the lid substrate wafer by heating, voltage is applied between the bonding film and the electrode plate to flow current in the lid substrate wafer and thereby cause an electrochemical reaction at the interface between the bonding film and the bonding face of the lid substrate wafer, thus anodically bonding the two to form bonded wafers.
The bonded wafers are then cut at predetermined positions to form a plurality of product packages (see, for example, JP-A-2006-339896).